1. Field of the Invention
This invention relates to an electro-luminescence display (ELD), and more particularly to an electro-luminescence display device that is adaptive for reinforcing its strength.
2. Description of the Related Art
Recently, there have been developed various flat panel display devices reduced in weight and bulk that is capable of eliminating disadvantages of a cathode ray tube (CRT). Such flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP) and an electro-luminescence (EL) display, etc. There have been actively processed studies for attempting to make a high display quality and a large-dimension screen of the flat panel display device.
In such flat panel display devices, the PDP has drawbacks in that it has been highlighted as the most advantageous display device to make a light weight, a small size and a large dimension screen because its structure and manufacturing process are simple, but it has low light-emission efficiency and large power consumption. On the other hand, the active matrix LCD employing a thin film transistor (TFT) as a switching device has a difficulty in making a large dimension screen because it is fabricated by a semiconductor process, but has an expanded demand as it is mainly used for a display device of a notebook personal computer. However, the LCD has a drawback in that it has a difficulty in making a large dimension screen and it has large power consumption due to a backlight unit. Also, the LCD has characteristics of a large light loss and a narrow viewing angle due to optical devices such as a polarizing filter, a prism sheet, a diffuser and the like.
On the other hand, the EL display device is largely classified into an inorganic EL device and an organic EL device depending upon a material of a light-emitting layer, and is a self-luminous device. When compared with the above-mentioned display devices, the EL display device has advantages of a fast response speed, large light-emission efficiency, a large brightness and a large viewing angle.
Referring to FIG. 1, an organic EL device 1 of the EL display devices has an anode electrode 4 formed from a transparent electrode pattern on a substrate 2, and a light-emitting organic compound layer 18 formed thereon.
The anode electrode 4 is formed from any one of indium-tin-oxide (ITO), indium-zinc-oxide (IZO) and indium-tin-zinc-oxide (ITZO), etc. on the substrate 2 by a photolithography. Such an anode electrode 4 is used as a data electrode.
The organic compound layer 18 has a hole injection layer 6 and a hole carrier layer 8 sequentially formed on the anode electrode 4. A light-emitting layer 10 having a light emission function is provided on the hole carrier layer 8. Further, an electron carrier layer 12 and an electron injection layer 14 are sequentially formed on the light-emitting layer 10.
A cathode electrode 16 formed from aluminum (Al) having a high reflectivity is provided on the organic compound layer 18.
In the organic EL device, a driving voltage and current are applied to the anode electrode 4 and the cathode electrode 16, and then holes within the hole injection layer 6 and electrons within the electron injection layer 14 are progressed into the light-emitting layer 10 to thereby excite a phosphorous material within the light-emitting layer 10. A picture or an image is displayed by a principle in which a visible light generated from the light-emitting layer 10 in this manner is emitted out through the transparent anode electrode 4.
A life of the light-emitting layer 10 of the organic EL device is critically influenced by damages of the cathode electrode 16 and the organic compound layer 18 caused by moisture and oxygen in the atmosphere. In order to solve this problem, an encapsulation process utilizing a packaging plate formed from a material such as metal or glass, etc. is added.
Referring to FIG. 2, the conventional packaging plate 30 is formed from glass, plastic or canister, etc. The packaging plate 30 includes a first face 32 provided with a getter 27 for absorbing moisture and oxygen, a second face 34 having a sealant 22 coated at the edge thereof, and a connection face 36 for connecting the first and second faces 32 and 34 such that the first and second faces 32 and 34 have a desired height of step coverage.
The first face 32 is provided with the getter 27 made from barium oxide (BaO) or calcium oxide (CaO) so as to absorb moisture and oxygen. Herein, in order to prevent the getter 27 as a moisture absorbent from being dropped on the organic compound layer 18, a semi-transmitting film (not shown) is attached onto the first face 32 such that moisture and oxygen, etc. come in and out. The semi-transmitting film is formed from Teflon, polyester or paper, etc.
The second face 34 is joined with the sealant 22 coated onto the edge of the substrate 2, thereby attaching the package plate 30 onto the substrate 2. The second surface 34 of the packaging plate 30 is joined with the substrate 2 by the sealant 22 to make a vacuum state, thereby preventing a life of the EL device from being critically influenced by damage of the cathode electrode 16 and the organic compound layer 18 caused by moisture and oxygen in the atmosphere. Herein, the sealant 22 is made from an ultraviolet-curing epoxy, etc. This ultraviolet-curing epoxy allows the substrate 2 or the packaging plate 30 to be pressurized and joined by a technique such as a dispensing and a printing, etc. and then is cured by an irradiation of an ultraviolet ray. Subsequently, after a sealing was made by the sealant 22, the organic EL device is filled with an inactive gas with no moisture or oxygen. To this end, a glove box or a vacuum chamber is used.
The connection face 36 allows the first face 32 provided with the getter 27 and the second face 34 attached onto the substrate 2 to have a desired height of step coverage, thereby causing an internal space of the package plate 30 to be made into a vacuum state. In this case, the connection face 36 may vertically connect the first face 32 with the second face 34, or may connect the first face 32 with the second face 34 in such a manner to have a desired slope.
However, such a packaging plate 30 has a problem in that it has a low strength because the first face 32 provided with the getter 27 takes a flat structure. Particularly, there is raised a problem in that, when a size of the packaging plate 30 is enlarged, it has a low strength because the first face 32 takes a flat structure, thereby causing a twist of the packaging plate 30.